Intravascular catheters such as angiographic catheters are introduced from the exterior of a patient into an artery or vein. After such introduction, the catheter is advanced and maneuvered through the arteriovenous system to a desired site, which may be an area of arterial stenosis, or an area from which x-ray contrast media is injected into the system, or the interior of the heart itself, for example. As described for example in Stevens U.S. Pat. No. 4,000,739, such catheter may be emplaced by first inserting a hollow needle with a trocar through the skin into the lumen of the desired blood vessel. Following this, a guide wire is passed through the needle and advanced up the artery or vein toward the area or the organ to be studied. The needle can then be removed, leaving the guide wire in the vessel.
Following this, a catheter introducer comprising a tubular sheath and a removable, hollow stylet or dilator unit may be advanced together over the wire into the vessel. Then, the guide wire and the dilator unit are removed, leaving only the sheath of the catheter introducer member present in the vessel.
Then, the desired catheter can be advanced through the sheath into the vessel.
The sheath of the catheter introducer typically carries a hub with hemostasis valve means on its proximal end to avoid uncontrolled bleeding and air embolism. The dilator unit, and then the catheter, pass through this hemostasis valve, the design of which is well-known and currently in commercial use.
As described for example in Furukawa et al. U.S. Pat. No. 4,850,975 a problem exists in the conventional technology of catheter introducers, in that the sheath which surrounds the dilator unit is subject to kinking, burring, or notching. One example of this is particularly illustrated in FIG. 11 of the Furukawa et al. patent, in which the distal end of the thin catheter introducer sheath is shown to be drawn away from intimate engagement with the dilator unit by the mechanical action of sheath advancement or the like. This happens because the sheath is desirably made as thin as possible, and, in the prior art, the sheath is typically made of a plastic which is only partially flexible to achieve self supporting characteristics, and thus is subject to kinking if it is bent unduly without internal support. Also, "burrs" can form on the proximal edge of the catheter introducer sheaths of the prior art, as described in the Furukawa et al. patent. Such burrs or irregularities, if formed in the catheter introducer sheath, can damage blood vessel linings or the like, and are quite undesirable.
However, sheaths made of more flexible elastomers or the like to avoid kinking would lack desired hoop strength, and thus would be even less useful.
As shown in FIG. 12 of the Furukawa et al. patent, another attempted prior art solution to avoid such burring and the like is to simply thicken the wall of the catheter introducer sheath and to bevel its proximal end. However, this also has its significant disadvantages, chiefly the fact that it is important for the sheath to be of a minimum thickness. An increased sheath thickness of course expands the puncture hole in the blood vessel and makes hemostasis more difficult.
The suggested solution of the Furukawa et al. patent includes the use of a dilator unit which defines a longitudinal slit to provide transverse elastic deformation action to the dilator unit. This, however, requires the use of a dilator unit that is more expensive to manufacture, and it exhibits other disadvantages that have restricted the commercial use of the Furukawa et al. invention.
The notching, kinking, or burring that takes place at the distal tip of the catheter introducer sheath occurs most frequently when the catheter is inserted through scar tissue or bent acutely during insertion. To summarize, a primary reason for this undesirable characteristic is that the sheath material is forced outwardly from its close-fitting relation with the dilator unit during the insertion process, because the plastic material of the thin, tubular sheath lacks the desired hoop strength to avoid slight, undesired radial stretching at the distal tip during the insertion operation. However, many plastics which have higher hoop strengths are undesirably stiff, and thus would exhibit other disadvantages as a material for manufacturing a catheter introducer sheath.
In accordance with this invention, a catheter introducer sheath is provided which is highly flexible and strongly resistant to kinking, but also exhibits a surprisingly high hoop strength to avoid radially outward stretching of the distal tip thereof, despite the great overall flexibility of the tubular sheath. For example, with the preferred tubular sheath of this invention when it does not contain a catheter or dilator unit, it is possible to tie a loose, overhand knot in without kinking anywhere along the tubular sheath, so that the lumen remains open. This is quite impossible with the presently used catheter introducer sheaths. When it is attempted, the stiffer, prior art sheaths kink, collapsing the lumen at various positions, and often leaving a permanent crease in the sheath wall from the attempt.